_ctypes fails to extend the return value per libffi contract

Bug report

Bug description:

The current implementation is relying on restype->size to write the data into a buffer, however, per libffi contract

integral types narrower than the system register size are widened

Which is not happening here. This has caused a failure on s390x when using libclang. cindex.py calls into libclang through ctypes, which builds the callback closures using libffi. With a c_int return, ctypes writes only the low 32 bits and skips the extension that both the ABI and libffi's closure contract require.

We have also opened a PR to fix this temporarily under llvm: https://github.com/llvm/llvm-project/pull/221024

CPython versions tested on:

3.11

Operating systems tested on:

Linux

Linked PRs

• gh-157045

Inizia in Modules/_ctypes/callbacks.c, nella gestione collegata del valore restituito, e leggi il contratto delle closure di libffi a cui si fa riferimento. Riproduci o esamina il comportamento della callback c_int su s390x, quindi verifica che i valori restituiti integrali stretti seguano l’estensione ABI richiesta invece di limitarsi a copiare restype->size byte. Controlla il PR di CPython collegato per il lavoro già in corso.